Disallow boolean test on promise

[burtonator]

Rule Suggestion

Is your rule for a general problem or is it specific to your development style?

General problem.

What does your suggested rule do?

Prevents an always positive boolean test.

List several examples where your rule could be used

if you have a Promise disallow an if test against it.

It will ALWAYS return true and is almost certainly not what you want. You almost certainly want to await it first.

This just bit me hard and I spent 2-3 hours trying to track this down before I realized my mistake.

[JoshuaKGoldberg]

Duplicate of #3983; should be better documented per #4117.